Understanding tumor invasion and metastasis provides crucial information with respect to carcinoma progression. Towards this goal, we have identified a mesodermal gene, Twist, which has a crucial role in promoting breast cancer formation. Earlier results from this laboratory have indicated that over-expression of Twist, a basic helix-loop-helix transcription factor, in MCF-7 breast cancer cells promotes tumorigenesis and increased vasculature and permeability within the tumor microenvironment of xenografts. Preliminary data have indicated that over-expression of this transcription factor can promote the expression of the choline kinase, a marker related to malignant transformation and metastasis. In addition, the activity of the increased levels of choline kinase is evident from the elevated levels of phosphocholine and total choline containing compounds in these transgenic cells. The present proposal is designed to understand the role of Twist in promoting breast cancer invasion and metastasis by altering the cellular physiology and biochemistry of breast epithelium by using functional imaging techniques. The three specific aims are: 1) To identify biochemical and physiological alterations in orthotopic tumors using Twist over-expressing breast cancer cells by functional magnetic resonance imaging and spectroscopy, 2) To functionally characterize and image the effects of down- regulating Twist in breast cancer xenograft models, and 3) To identify novel metastatic markers in Twist over-expressing cells and to validate them in breast cancer patient samples. In this study, we will use functional magnetic resonance imaging to identify the molecular changes that influence the phenotypic characteristics of breast tumors, such as, changes in choline containing compound levels, lactate levels, extracellular pHe, vascular volume and permeability surface area product in Twist over-expressing as well in Twist down-regulated cells. Also, we will use non-invasive optical imaging to identify various stages of cancer progression using MCF-7/Twist cells transfected with an optical reporter gene (tdTomato). Finally, the gene signature patterns identified using the preclinical model will be applied to patient samples in order to identify potential markers of breast cancer progression. In the long term, these studies will help in the pathological diagnosis of breast cancer and provide insights that will contribute to the development of novel imaging markers and chemotherapeutic drugs for breast cancer.